1.1 Field of the Invention
The present invention relates generally to the transmission of data services over a geosynchronous satellite communications network, and more, in particularly, relates to the transmission of services to satellite communications networks having Direct-To-Home (DTH) satellite receivers including a single-LNB (Low-Noise Block) in the outdoor unit (ODU) antenna assembly.
1.2 Description of Related Art
1.2.1 Direct-To-Home Satellite Television Reception
As is well known in the art, the signals broadcast from a geosynchronous, DTH satellite are sent on one of two polarizations, which allows two sets of signals to be carried by one frequency band. In order to receive an analog TV program or digital carrier, a receiver must select the proper polarization (rejecting all signals on the other polarization) and tune to the appropriate frequency.
FIG. 1 illustrates the receive portion 10 of a typical satellite DTH satellite system.
A home is typically equipped with:
An ODU 11 including:
An antenna mount 12, which holds the remainder of the ODU 11 in a fixed position so that signals can be received from a single, geosynchronous orbital position.
A parabolic reflector 14, which gathers received signals from a single geosynchronous orbital position and passes the concentrated signals to a feed horn (FH) 16.
FH 16 takes the concentrated signals from the parabolic reflector 14 and passes them to a single-LNB 18.
The Single-LNB 18:
selects one of the two sets of polarized signals from the geosynchronous orbital position at the direction of a set-top box 13.
low-noise amplifies the complete frequency band,
translates the amplified signals to L-Band (e.g. 950 Mhz to 2150 MHz) and
passes the resulting signals via a coaxial cable 17 to the set-top box 13.
The Coaxial Cable 17 carries the L-band satellite receive signals to the set-top box 13. The coaxial cable 17 carries power and polarization selection from the set-top box 13 to the single-LNB 18.
The Set-Top Box 13 allows the end-user of TV 14 to select a single TV channel from those receivable by the ODU 11. The set-top box 13 converts the TV channel from its satellite broadcast form to the form accepted by an unmodified broadcast television (e.g. NTSC or PAL) and passes the signal to the TV 14.
The set-top box 13 passes the polarization selection to the single-LNB 18 through the coaxial cable 17 in different ways, depending on the type of single-LNB 18. Some single-LNBs receive the desired polarization by detecting the presence or absence of a 22 kHz tone on the coaxial cable 17. Other single-LNBs receive the desired polarization by measuring the dc voltage received on the coaxial cable 17. Still other single-LNBs receive the desired polarization in other ways, but always from signals on the coaxial cable 17.
FIG. 1 describes a vast majority of the over 40 million Direct-To-Home receivers currently in use. A major cost factor with the system in FIG. 1 is that the installation of the ODU 11 and coaxial cable 17 is typically beyond what a normal consumer would consider doing on their own and is typically done at significant expense by a professional installer.
1.2.2 Digital Satellite Direct-To-Home Systems
As is well known to those skilled in the art, typical DTH systems are designed so that multiple digital services (e.g. television, audio and other services) are multiplexed into a single multimegabit per second digital carrier. The multiplexing is performed by means of fixed-length packets such as the 188-byte packets defined by what is known as the MPEG-2 transport system and as defined in the International Standards Organization (ISO) standard ISO 13818 Part 1, the contents of which are hereby incorporated by reference. Forward error-correcting codes are utilized at the bit level so that, under normal weather conditions, data is virtually never lost.
Each 188-byte MPEG-2 transport packet contains an address field, referred to as a program identifier (PID), which uniquely identifies the service carried by the packet. Digital DTH systems deliver a service""s packets in order even though the multiplexing and remultiplexing of services may result in the resequencing of packets from different services.
Digital Video Broadcast (DVB), a European standards body, has defined standards for carrying data services over MPEG-2 transport systems. Three of these standards are:
Data Pipingxe2x80x94where an individual packet ID (PID) carries a byte stream within the 184 byte payload field of the 188-byte MPEG packets.
Data Carouselxe2x80x94the DVB standard multicast file transfer mechanism where given files are repeatedly transmitted so that if the receiver is unavailable when a file is first transmitted or the first reception is errored, the receiver can come back and receive a substantial transmission.
Multiprotocol Encapsulationxe2x80x94where collections of internet protocol (IP) packets, typically IP multicast packets, are carried within the payload fields of MPEG packets in a standard way.
1.2.3 Digital Satellite Direct-To-Home Data Services
Various kinds of data services can be delivered to end-users via digital satellite DTH systems. These services can typically be categorized as follows:
Multicast file transferxe2x80x94the delivery of complete files of digital data containing software, Internet Web pages, digital music, etc. For most multicast file transfers, the data is not extremely real-time. That is, the transmitter has some flexibility regarding when the multicast file transmission takes place. A partial or errored reception of a multicast file transfer is of no use to the receiver.
Carouselxe2x80x94this is a variation on the multicast file transfer where given files are repeatedly transmitted so that if the receiver is unavailable when a file is first transmitted, or the first reception is errored, the receiver can come back and receive a subsequent transmission.
Streaming multicast mediaxe2x80x94examples of this category include streaming digital audio and video. Streaming multicast media contains a characteristic whereby a user typically joins a stream in the middle of its transmission, and the transmission is useful even when not received completely from beginning to end and even in the presence of occasional errors.
Unicast alertxe2x80x94examples of this include sending of xe2x80x9cpagesxe2x80x9d or e-mail arrival notifications. This category is exemplified by the transmission of a small number of packets to a single end-user where the data transmitted must be received by the intended user with high-probability. Often unicast alerts are made robust against transmission errors by means of repeat transmission.
These kinds of data services can be carried either natively via data piping or data carousels or some other similar mechanism or can be carried via IP packets and multiprotocol encapsulation.
1.2.4 Digital Satellite Reception
FIG. 2 illustrates the digital reception part 20 of a typical digital satellite receiver 23.
The digital reception part 20 includes an ODU 11, a coaxial cable 17, and a digital satellite receiver 23. The ODU 11 further includes an antenna mount 12, a parabolic reflector 14, an FH 16, and an LNB 218. The digital satellite receiver 23 further includes a tuner 232, a demodulator/forward error correcting (FEC) decoder 234, and a controller 236.
As discussed above with respect to FIG. 1, the LNB 218 translates the signals from the satellite to L-band. As is well known to those skilled in the art, a particular LNB somewhat inaccurately performs this translation. The combination of unit-to-unit and temperature variation typically allows the translation to be inaccurate by approximately xc2x14 MHz.
The term xe2x80x9cacquirexe2x80x9d, in the context of satellite digital receivers, refers to the process of obtaining successful reception of a digital carrier. When a signal is xe2x80x9cacquiredxe2x80x9d, it is being received. If acquisition is lost, then the signal is no longer being received and must be re-acquired.
In order to acquire a typical satellite digital carrier, the receiver 23 must have a specification of the kind of signal it is attempting to receive. Herein, the term receive parameters refers to this specification for a digital carrier. For DTH digital satellite carriers which conform to Digital Video Broadcast (DVB) standards, the set of receive parameters may include the polarization, symbol rate, the FEC rate and frequency. Some satellite receivers 23 can determine the FEC rate dynamically and therefore, this need not be specified.
In order to acquire a typical satellite digital carrier, the receiver 23 must tune precisely to the frequency of the carrier as it passed to the carrier by the coaxial cable 17. In order to retain acquisition, the receiver 23 must precisely track the frequency of the carrier as seen by the demodulator/FEC decoder 234.
The tuner 232 of the digital satellite receiver 23 selects a single portion of the entire L-band received from the LNB 218, translates it to a single center frequency (typically baseband), and forwards it (as signal 231) to the demodulator/FEC decoder 234. The controller 236 of the digital satellite receiver 23 controls the tuner 232 to select the frequency to be xe2x80x9ctunedxe2x80x9d.
The demodulator/FEC decoder 234 then attempts to precisely match the tuned frequency to match the center frequency of the digital carrier to be received. The demodulator/FEC decoder 234 commands the tuner 232 to make small adjustments to the tuned frequency by sending an automatic frequency control (AFC) signal 233 to the tuner 232.
When the receiver 23 is first attempting to acquire a carrier, the controller 236 coordinates the acquisition by commanding the tuner 232 and demodulator/FEC decoder 234 to successively search the range of frequency uncertainty caused by the LNB""s 218 inaccurate translation. The search is commanded to take place in the form of a series of fixed-width frequency steps. For each search step, the demodulator/FEC decoder 234 then searches for the signal adjusting the AFC signal to search the frequency range within the step.
The demodulator/FEC decoder 234 reports signal reception status to the controller 236. When acquisition is obtained and completes successful reception, the demodulator reports to the controller 236 its estimate of the signal""s center frequency within the tuning step set by the controller 236. The controller 236 can thus calculate the frequency offset, which is the difference between where the signal should be, given perfect translation by the LNB 218 and tuner 232, and where the signal actually is.
The controller 236 uses this frequency offset to speed reacquisition when the satellite receiver 23 is switching from one digital carrier to another, perhaps on a different polarization. The controller 236 can use the frequency offset to command the tuner 232 and the demodulator/FEC decoder 234 to search for the new signal within a much smaller region of uncertainty. The result is that it takes a much shorter time to acquire the signal than would be possible when searching the entire range of frequencies possible with LNB translation error.
1.2.5 Packet-Level Forward Error Correcting Codes
As is well known to those skilled in the art, FEC codes are useful for increasing the reliability of transmission across error-prone transmission channels. Packet-level FEC codes are useful on packet networks where there is an intolerable level of packet loss, but lower layer protocols prevent the processing of errored packets by detecting and discarding errored packets. Packet-level FEC codes need only correct loss of packet (erasures) and need not correct errored packets.
Repeat transmission is the simplest form of packet-level FEC. Each packet is sent multiple times so that the satellite data receiver 20 need only receive one of the various transmissions.
Exclusive-OR parity is another simple form of packet-level FEC, which works well with equal length packets and can easily be extended to work with variable-length packets. With exclusive-OR parity, a parity packet is formed by calculating the Exclusive-OR sum of a group of packets. Any single lost packet may be reconstituted by calculating the Exclusive-OR sum of the parity packet and all of the group""s other packets.
Exclusive-OR parity can handle single, isolated lost packets. Many communications channels do not experience isolated packet loss. Instead they experience bursts of errors where many or all packets are lost for a period of time. As is well known to those skilled in the art, interleaving may be used to make a burst of errors have an effect similar to a series of isolated packet losses and, as a result, be correctable by error-correcting codes.
A simple form of Exclusive-OR parity combined with interleaving is referred to herein as Blocked Exclusive-OR Parity FEC. Blocked Exclusive-OR Parity FEC is illustrated in FIG. 3. The interleaving groups each set of N packets together as a single block and then performs Exclusive-OR parity on each group of M blocks. FIG. 3 illustrates a sample rate 3/4 blocked exclusive-OR parity FEC where the block size is 6 packets and where the exclusive-OR parity FEC is one parity packet for every 3 data packets. Any burst loss of less than or equal to 6 packets can be corrected provided the burst loss occurs no more frequently than once every 24 packets. In general, this code can correct any single burst loss of less than N packets out of any M*N packets.
As is well known to those skilled in the art, advanced packet-level FEC codes may be constructed so that a file can be reconstituted with extremely high-probability provided the overall packet loss rate is less than a designed threshold regardless of the set of packets lost.
1.3 Direct-To-Home Satellite Television/Data Reception
FIG. 4 illustrates the conventional home system 30 required where data reception and television reception are required simultaneously. FIG. 4 is very similar to FIG. 1, with the exception of the addition of a second coaxial cable 17xe2x80x2 and a satellite data receiver 15, and the replacement of the single LNB 18 with a dual LNB 318.
These modifications are required as the satellite data services are typically transmitted on a single, unchanging polarization while the set-top box 13 is changing its LNB""s polarization from moment to moment as it the viewer changes channels.
In order to upgrade from the receiver 10 of FIG. 1 to the system 30 of FIG. 4, the receiver 10 requires three non-trivial expenses beyond the addition of the satellite data receiver 15:
1. Replacement of the single-LNB 118 with the dual LNB 318, which means an additional hardware cost.
2. Addition of a second coaxial cable 17xe2x80x2, which also means an additional hardware cost.
3. Professional installation of 1 and 2, which is an additional cost and also requires the homeowner to be available to let the installer in.
With modem satellite data receivers 15, the above expenses exceed the cost of the satellite data receiver 15 and, combined with the inconvenience of letting the installer in have been a major obstacle to the successful launch of broadcast satellite consumer data services.
The present invention solves the above identified problems with conventional home receiver systems by providing a satellite data receiver and/or satellite data receiver controller, which eliminates a need to upgrade the outdoor unit and which does not require an installer to enter the consumer""s home.
The present invention, in its various embodiments, is directed to a satellite data receiver, a satellite data receiver controller, a method, an article of manufacture, and a propagated signal, which permits the user of a conventional satellite television system to receive data services, other than televised signals, without upgrading their outdoor unit or requiring an installer to be let in to the consumer""s home. The satellite data receiver and/or satellite data receiver controller of the present invention achieves this goal by performing one of the following functions:
tracking another receiver""s polarization selection signals and receiving data simulcast on carriers on each of the polarizations;
tracking another receiver""s polarization selection without monitoring the polarization selection signals by searching for a simulcast transmission on the receiver parameters for a pair of carriers, one on each polarization;
tracking another receiver""s polarization selection signals and, in most cases, passing the track selection signals to the single LNB, but in some cases, overriding the selection signals; or
tracking a first satellite data receiver""s acquisition status and setting the satellite data receive parameters in such a way as to track the polarization shifts from a second satellite receiver and allow reception of data services simultaneously transmitted on both polarizations.
In some embodiments of the present invention, the functionality which permits the satellite data receiver and/or satellite data receiver controller to execute the above functions is built in; in other embodiments, the functionality is loaded via conventional software program or downloaded via a propagated signal.
The present invention in its various embodiments also utilizes one of several error-correction decoding techniques in order to avoid data loss during a polarization switch. These decoding techniques include repeat transmission, exclusive-OR parity codes, blocked exclusive-OR parity codes, phase burst correcting array codes, general array codes, Reed-Solomon codes, low-density parody check codes, and cyclic codes.